1. Field of the Invention
In fluid systems, particularly high pressure fluid system, it is frequently desirable to employ a control valve which is, and will remain, substantially leakproof despite erosion of metal surfaces, corrosion, and the presence of particulate matter in the contained fluid. Conventional metal-to-metal valve seats may initially be leakproof, but under the influence of such erosion, corrosion, and similar damage to valve seating surfaces they quickly begin to leak when closed and require repair or replacement. This invention provides a solution to the problems encountered when such conventional valves are employed.
2. Description of the Prior Art
Prior art valves having soft nonmetallic seating surfaces are typified by those disclosed in U.S. Pat. No. 2,060,748 to Roberts et al., U.S. Pat. No. 3,327,991 to Wallace, U.S. Pat. No. 3,410,524 Self, and 3,809,362 to Baumann. In each of the valve seat arrangements disclosed by these references, a soft polymeric or elastomeric seat ring, which is generally annular in shape, is partially confined in an annular space surrounding a valve inlet passageway. This annular space is bounded in the radially outer direction by the valve body, and in the radially inner direction by a sleeve member which is slidable in the valve inlet passageway to compress and deform the annular seal ring. The seating surface of the prior art seal ring is, or becomes upon axial movement of the sleeve member, exposed for contact with the seating surface of a valve plug member, a portion of the valve plug member serving as a piston which engages and moves the sleeve member axially to effect compression of the resilient seal ring as the valve plug member is moved to a valve-closing position.
In these prior art valves it is the resilience of the deformable seal ring which provides the force to restore the sleeve member to its original position when the valve is reopened. For this reason, the sleeve member may not always be returned to the same position each time the valve is opened or closed, inasmuch as the original volume, shape, or resiliency of the seal ring may be substantially altered through use. For example, the seal ring may cold-flow if manufactured of a fluorocarbon polymer such as polytetrafluoroethylene. Moreover, in these prior art seals the seal ring commonly extends a substantial distance in the direction of the axis of the valve inlet passageway so that changes in temperature of the fluid flowing through the valve may result in significant thermal expansion or contraction of the seal ring which is detrimental to valve performance.